Volkswagen, Audi Direct Fuel Injection System

Volkswagen, Audi Direct Fuel Injection System

For the past decade, almost every vehicle that Volkswagen and Audi has sold in the U.S. has been equipped with direct fuel injection. These FSI, TSI and GDI systems allow for better fuel economy and power. The switch to direct injection has also allowed Volkswagen to downsize its engines from 2.0L to 1.4L on base models without losing any power, while still improving fuel efficiency.


For the past decade, almost every vehicle that Volkswagen and Audi has sold in the U.S. has been equipped with direct fuel injection. These FSI, TSI and GDI systems allow for better fuel economy and power. The switch to direct injection has also allowed Volkswagen to downsize its engines from 2.0L to 1.4L on base models without losing any power, while still improving fuel efficiency.

By directly injecting fuel into the cylinder, the system avoids the inconsistencies of fuel splashing onto the back of an intake valve. Direct fuel injection, coupled with variable valve timing and variable intake manifolds, maintains better control of the volume of air and fuel injected into the cylinders.

The injectors also do a better job of controlling droplet size, compared to a system that forces the fuel and air to go around an intake valve. This creates no chance for a large drop of fuel to slide down the valve and into the cylinder. This control also means reduced cold-start emissions and the engine enters into a closed-loop condition sooner than with port fuel-injection systems.

How Does it Work?
Pressure is the key to making the Volkswagen direct-injection system work. With more than 3,000 psi on the backside of an injector under some conditions and combustion pressures on the other side, managing what is happening at the tip of the injector is critical.

Most Volkswagen direct-injection systems use a capacitor and voltage inverter to create voltages that can range from 40 to 100 volts. One of the best ways to view the output of the driver and actuation of the injector is using an inductive amp/current clamp and a scope. Some later systems use a peak/hold signal to the injector.

If the ECM detects a problem, it will shut down the injector and driver for the sake of self-preservation. This is why, on some systems, it may be impossible to observe a faulty injector in operation. A direct injector is under a lot of pressure, so leaks can occur. For example, leaks may occur when the engine is resting, which will cause severe carbon buildup and a rich fuel reading.

When an injector is not firing, the affected cylinder becomes an air pump that forces large amounts of oxygen past the air/fuel ratio sensor. This can be viewed using a scope. The ECM can match the exhaust pulse to engine timing to determine the faulty cylinder.

VW and Audi positioned the injectors directly into the combustion chambers for greater efficiency. The new B7 platform A4 and Passat had an in-tank fuel pump. They also had a camshaft-driven, mechanical high-pressure fuel pump that ran the fuel pressure as high as 3,000 psi. The in-tank pump provides the correct volume of fuel in this returnless system. The pump on the camshaft controls the pressure at the fuel rail.

FUEL-RELATED DTCs
The Audi A4 and Passat models came out with direct injection in 2006. The hardening of the camshafts was insufficient and excessive wear could occur, causing the MIL to come on and DTC P2293 to be stored in the ECU. This code was for fuel pressure regulator 2 performance. Sometimes, DTCs P0087 (fuel pressure too low) and P1093 (fuel trim bank 1 malfunction) would also be stored.

The engines that were affected were the Audi 2.0L turbo (BPG) and the VW 2.0L turbo (BPY) (see Photo 1). The earliest TSB I found addressing the issue was from June 18, 2007.

Photo 1

If you suspect the car you’re working on has this issue, the high-pressure pump will need to be removed to determine the extent of the damage to the cam follower, the camshaft or even the pump itself.

1. Remove the pump to inspect the follower only when the engine is cold, and be sure to release the high pressure before disconnecting the lines.

2. Start the car and disconnect the plug to the fuel pressure regulator on top of the pump. Let the car idle for about 10 seconds and the pressure will drop from 120 bar to 6 bar.

3. Shut off the engine and immediately disconnect the fuel lines. Disconnect the low-pressure sensor and remove the three bolts that hold the pump in place (see Photo 2).

Photo 2

4. Carefully remove the pump. The cam follower may stay in the cylinder head. Take a look at the pump and follower, and determine if there is abnormal wear that needs to be addressed (see Fig. 1). The pump can be reused, unless the follower is completely worn through, causing direct contact with the cam lobe (see Figures 2 and 3).

Figure 1: Cam followers in various stages of wear: holed base (A), excessive wear (B), normal wear (C) and new part (D).
Figure 2: Excessive wear on the lobe for the high-pressure fuel pump in the intake camshaft.
Figure 3: Excessive wear marks on the tip of the high-pressure fuel pump plunger.

5. If the follower is excessively worn, carefully inspect the cam lobe to determine if the intake camshaft will need to be replaced. If the camshaft needs to be replaced, there is a new camshaft (P/N 06f109101b) that has increased hardening of the camshaft lobe.

6. When replacing the camshaft, it would also be a good time to replace the timing belt, water pump and tensioner, unless the car has very low mileage.

7. When reinstalling the fuel pump, always replace the sealing O-ring. Install the new follower into the cylinder head and rotate the engine until the follower is down as far as it will go.

8. Replace the O-ring for the pump and carefully insert the pump into the follower in the cylinder head. Tighten the three bolts in a diagonal sequence and torque them to 10 Nm.

9. Install the feed and return lines and torque the supply line to 30 Nm and the return line to 25 Nm. Check to make sure there is no stress on the lines.

10. Connect the low-pressure sensor and pressure regulator, and then start the car and double-check for leaks.

Even if the intake camshaft needs to be replaced, the job is not difficult and doesn’t require any special tools, other than the ones you would already have when doing a timing belt; it’s just time consuming. Addressing the carbon buildup and stuck flaps in the intake is also not difficult. Your on-line service information system will have procedures for diagnosing and repairing the issues with the early direct-injection cars.

Engine Oil Specs and Carbon
The oil in the crankcase of a direct-injected Volkswagen engine can make a huge difference in the health of the engine. The right oil can reduce carbon deposits on the intake valves and keep the engine healthy. Volkswagen has recommended specific oil grades that meet proprietary requirements in recent years for its turbocharged and direct-injected engines. These are not to be ignored if you are changing the oil on a direct-injection engine.

Most conventional oils have high volatility numbers. If oil has a high-volatility number, it vaporizes more quickly when exposed to heat. This means that the oil can become thicker over time and won’t lubricate as well. It also means that there is a greater volume of oil vapor that the PCV system in a Volkswagen engine has to process. These vapors can be loaded with hydrocarbons and stick to the intake valves, causing a carbon deposit problem. Synthetic oils have a much lower oil volatility. This reduces the amount of oil vapor and the possibility of carbon deposits forming on the intake valves.

It is difficult to avoid Volkswagens with direct fuel injection. They represent a large percentage of the Volkswagens on the roads today. The key to servicing these vehicles is service information and training. They are not difficult to service and offer new opportunities that were not around 15 years ago, like engine decarbonization and servicing high-pressure fuel pumps.

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